1. Field of the Invention
The present invention relates to telecommunications, and, in particular, to provisioning for the restoration of service in distributed optical telecommunication networks.
2. Description of the Related Art
Rapid advances in optical networking are expected to provide network operators with new tools such as optical-layer restoration (OLR) at relatively low cost to enhance the reliability and versatility of transport networks. With the availability of large optical cross-connects, OLR for mesh networks would provide a very attractive solution for restoration of large optical networks. OLR should support services with heterogeneous data network platforms and be transparent to data line-card bit rate. Due to the omnipresence of SONET (Synchronous Optical NETwork) rings and their associated fast protection/restoration, network operators now expect mesh restoration to be xe2x80x9cring competitive,xe2x80x9d which implies a mesh restoration speed of a few hundred milliseconds as well as highly efficient sharing of restoration capacity among various links. While rings require an excess capacity of 100%, mesh restoration requires only 40-70%. Thus, shared mesh restoration would offer the potential of huge savings for the network operator.
A prototypical fiber transport mesh network for the continental United States may consist of about 100 nodes and over 170 links, where each link is capable of carrying optical signals in either direction between two corresponding nodes. In a WDM (wavelength division multiplexing) optical network, each link comprises one or more unidirectional and/or bidirectional optical fibers, each of which is capable of carrying multiple optical signals at different wavelengths.
Each node in such a mesh network may be configured with one or more optical cross connects (OXCs) that enable individual optical signals to be dropped, added, or continued. A dropped signal is received at a node from another node and transmitted to a local customer of the node. An added signal is received at a node from a local customer and transmitted to another node. A continued signal is received at a node from another node and transmitted to yet another node.
Provisioning refers to the process of configuring the cross-connects in the nodes of a network for a new demand to be satisfied by the network or the deletion of an existing demand, where the term xe2x80x9cdemandxe2x80x9d refers to a unidirectional transmission of signals from a start node to an end node in the network, possibly through one or more intermediate nodes. The path from the start node to the end node that satisfies the demand is referred to as the service path. In addition to being able to satisfy new demands and delete existing demands, a robust network should also be able to perform automatic provisioning to restore communications to satisfy a demand after the occurrence of a failure in a link along the service path for that demand. In particular, the network should be able to detect the existence of the failure and automatically reconfigure the cross-connects in the nodes of the network as needed to restore communications to satisfy the demand within a reasonable period of time (e.g., within a few hundred msec of the failure if not quicker) along a path, referred to as a restoration path, that bypasses the failed link.
The present invention is directed to techniques for the detection and communication of failures in networks, such as optical mesh networks, to enable automatic restoration of communications.
In one embodiment, the present invention is, at a node of a telecommunications network satisfying a demand from a start node to an end node, a method for automatically provisioning the network from a service path to a restoration path after a failure occurs in the service path, comprising the steps of (a) receiving, at the node, an indication of the occurrence of the failure in the service path; (b) if the node is an intermediate node of the service path, then transmitting, by the node, a failure message to its next node along the service path; (c) if the node is the end node of the service path, then transmitting, by the node, a restore message to its previous node along the restoration path; and (d) if the node is an intermediate node of the restoration path, then transmitting, by the node, a restore message to its previous node along the restoration path.
In another embodiment, the present invention is a node for a telecommunications network, comprising (a) a cross-connect connected to a plurality of input ports and a plurality of output ports and configurable to connect incoming payload signals received at an input port to outgoing payload signals transmitted at an output port; and (b) an operating system configured to receive an indication of an occurrence of a failure in a service path satisfying a demand from a start node to an end node, wherein, in order to automatically provision the network from the service path to a restoration path for the demand:
if the node is an intermediate node of the service path, then the operating system causes the node to transmit a failure message to its next node along the service path;
if the node is the end node of the service path, then the operating system causes the node to transmit a restore message to its previous node along the restoration path; and
if the node is an intermediate node of the restoration path, then the operating system causes the node to transmit a restore message to its previous node along the restoration path.